Descent of Edward IV

Professor Millar, in his *Historical View of the English Government* (ii. 174.), in discussing the claim of Edward IV. to the English throne, speaks of "a popular though probably a groundless tradition, that by his mother he was descended from Henry III. by an elder brother of Edward I., who, on account of his personal deformity, had been excluded from the succession to the crown." Where may I find this tradition? or where meet with any information on the subject?